add an option to run eb with a debugger such as pdb

[trz42]

Sometimes one needs to understand precisely what eb does, determine the values of variables and check the status of the filesystem. While eb can print lots of debug information that may not be enough.

One can run eb with a debugger, for example,

python3 -m pdb -m easybuild.main -S TensorFlow

but it would be more convenient to have a command line option such as --pdb or --debugger=pdb which would then run eb with corresponding arguments.

When running eb with pdb one might want to switch off Rich output (adding --output-style=basic). However, it could also be that running in a tmux session resulted in pdb not accepting commands or not showing them when they were typed.